The present invention pertains to the field of orthopedic surgery, and more specifically relates to an implantable device for lengthening, and also for correction of rotational and angular malpositions, of skeletal bones. The invention advantageously can be applied in connection with stabilization of fractures, post-traumatic bone defects, bone shortening, malpositions, congenital malformations and bone defects after tumor surgery.
Within the field of orthopedic surgery, it is known to use implantable devices for stabilizing fractures, lengthening skeletal bones, or for correcting different malpositions.
Many of the previously known devices require that suitable attachments means arc driven into the skeletal bone on both sides of the bone portion which is to be influenced, and that subsequently a screw assembly is applied between the attachment means, wherein a screw or the like acting on the screw assembly, alternatively on the attachment means, is allowed to protrude through the skin of the patient. Thereafter, by means of turning the screw, the length of the screw assembly can be influenced in accordance with an adapted lengthening scheme. Accordingly, in case it is desired to correct a malposition of a skeletal bone which for some reason occurs, by means of a surgical operation, a screw assembly of the above-described type can be applied at one side of the skeletal bone with the aid of two attachment means, whereafter the skeletal bone between the two attachment means can be cut off. By means of lengthening the screw assembly in accordance with the chosen lengthening scheme, a gradual ending of the skeletal bone in question can be obtained. Finally, after an appropriate healing time, the screw assembly, the screw and the attachment means can be removed by means of a surgical operation. In case only a linear lengthening is desired, several screw assemblies in parallel can be applied around the skeletal bone in question.
Furthermore, when stabilizing fractures, it is known to use intramedullary nails, which are inserted into the bone-marrow cavity of a tubular skeletal bone. During use, it is also know that such devices can be activated and/or controlled from the outside after the implantation and during lengthening action.
Accordingly, for example the patent publication U.S. Pat. No. 5,626,521 discloses a nail assembly for bone lengthening comprising a first nail body portion and a second nail body portion. The assembly farther comprises a power package inside either the first or the second nail body portion, wherein the power package comprises a power-supplied hydraulic pump which forces hydraulic fluid from a hydraulic fluid container and into a sealed chamber between the first and second nail body portions, thereby forcing the first nail portion to be extended longitudinally in relation to the second nail portion and increasing the length of the nail. It is also reported that the disclosed assembly may comprise a spring of a heat-sensitive memory material such as nitinol, and a heating system with a battery-powered electrical heater acting on the spring. According to U.S. Pat. No. 5,626,521, external activation and/or control of the assembly may be accomplished e.g. by means of providing the heating system with a timer or a suitable circuit for remote control which acts on the heating system.
Previously known arrangements for lengthening or correction of skeletal bones which require one or several permanent skin lead-throughs during the treatment time are associated with a large discomfort for the patient and a raised risk of infection.
The previously known implantable devices for lengthening and correction of skeletal bones which can be controlled from the outside, or which otherwise can be controlled without any permanent skin lead-throughs, often comprise a large number of mechanical and electronic components, and can be perceived as complicated or unnecessarily expensive.
When the external dimensions, the durability and the different lengthening properties are concerned, It may become expensive to tailor-make devices for each individual case in accordance with the prior art, since this often requires a number of the many different components to be re-dimensioned. Furthermore, when devices having small external dimensions arc concerned, problems with lack of internal space may arise.
Accordingly, a first object of the present invention is to provide a simple and reliable, implantable device for lengthening and correcting malpositions of skeletal bones, wherein the dimensions and the lengthening process of the device can be tailor-made in advance for the configuration and type of tubular skeletal bone in question into which the device is to be implanted, and where the device also can be designed with very small external dimensions thanks to its simple design.
The first object of the invention is achieved by means of the device having an elongate shape comprising a first end, a second end, a length dimension and a cross-sectional dimension, and the device further comprising a lengthening means for bringing the first and second ends into displacement from each other to a predetermined distance between each other after an activation. According to the invention, the lengthening means comprises an absorbent body, which is arranged for bringing the first and second ends to the predetermined distance by means of a controlled swelling after the activation while the length dimension increases more than the cross-sectional dimension.
A second object of the present invention is to provide an implantable device which, in addition to the above-mentioned advantages, also enables correction of rotational and angular malpositions of skeletal bones.
The second object of the invention is achieved by means of the absorbent body of the implantable device further comprising one or several stiffening elements and/or one or several swelling zones having a raised intrinsic swelling capacity in comparison to the remaining absorbent body, which arc arranged for controlling the swelling so that the first and second ends strive towards a predetermined angle in relation to each oilier after the activation.
Further object of the invention will become evident from the following description, while the features enabling these further objects to be achieved are evident from the attached, dependent claims.